The technical field of the invention is that of making and installing production risers for extracting oil, gas, or other soluble or fusible material or a suspension of mineral material from the sea bed via an undersea well head for the purpose of developing production fields installed at sea, off-shore. The main and immediate application of the invention lies in the field of producing oil.
A floating support generally comprises anchor means for remaining in position in spite of the effects of currents, winds, and swell. It generally also includes means for storing and processing oil and means for off-loading oil to shuttle tankers which call at regular intervals to take away the production. Such floating supports are known by the acronym FPSO which stands for “floating production storage off-loading”. The acronym is used throughout the description below.
Because of the large number of lines that exist in an installation of this type, hybrid tower type bottom-to-surface connections are implemented in which substantially vertical rigid pipes referred to as vertical “risers” are connected to the undersea pipe resting on the sea bed and rise up a tower to a depth that is close to the surface, from which depth flexible hoses provide a connection between the top of the tower and the floating support (FPSO). The tower is then provided with buoyancy means enabling it to remain in the vertical position, and the risers are connected at the foot of the tower to the undersea pipe by flexible sleeves which absorb the angular movements of the tower. The assembly is commonly referred to as a “hybrid” tower since it makes use of two technologies, firstly a vertical portion known as the “tower” in which the riser is constituted by rigid pipes, and secondly the top portion of the riser which is constituted by flexible hoses in catenary configurations providing the connection with the floating support (FPSO).
French patent No. FR 2 507 672 published on Dec. 17, 1982 and entitled “Rising column for great depths of water” describes one such hybrid tower.